1. Field of the Invention
The present invention relates generally to a cross connector for use in coupling spinal rods in a spinal fixation system and, in particular, to the manner of retaining and adjusting such spinal rods with respect thereto.
2. Description of the Related Art
As is generally known in the art, spinal abnormalities may be correctable using a pair of posterior spinal fixation rods attached to the vertebrae using pedicle screws and the like. In order to provide increased stability and rigidity, especially to resist twisting or the like, the pair of elongated rods often include cross connecting devices. The cross connecting devices typically traverse the spinal column and couple to each of the elongated rods. In other words, the cross connecting devices are perpendicular or substantially perpendicular to the spinal column.
One difficulty with connecting the elongated rods using such cross connecting devices resides in the fact that the pair of elongated rods is not exactly parallel and equally spaced along the spine. The cross connecting devices typically include at least two separate portions that couple together to compensate for these deviations. In order to accommodate the relative positions of the elongated rods, the cross connecting devices must be adjustable rotationally, angularly, and vertically. This typically involves adjusting and re-adjusting the various components of the cross connecting device related to the positioning thereof, which necessarily involves a trial and error approach. While this may be unavoidable, the constant need to loosen and tighten the locking or retaining mechanisms associated with such adjustments increases the time required to complete the operation.
Another difficulty encountered by cross connecting devices is the manner in which such devices are retained to the elongated rods. Some rod fasteners of cross connecting devices use threaded fasteners, such as a set screw or a nut, to attach the device to the adjacent rods. Such a threaded fastener must be tightened enough to prevent movement, but not be over tightened to the point that it causes damage to the rod. Certain configurations have also been disclosed to avoid potential damage created by point contact with the rods. Exemplary configurations are disclosed in U.S. Pat. No. 5,947,966 to Drewry et al., U.S. Pat. No. 6,136,003 to Hoeck et al., U.S. Pat. No. 6,283,967 to Troxell et al., U.S. Pat. No. 6,872,208 to McBride et al., U.S. Pat. No. 6,887,241 to McBride et al., U.S. Pat. No. 6,958,066 to Richelsoph et al., and published U.S. application 2006/0064093 to Thramann et al.
Thus, it would be desirable for a cross connector apparatus to be developed for use with a spinal fixation system which minimizes the number of fasteners required for adjusting the position of the apparatus with respect to the spinal rods. It would also be desirable for a cross connector apparatus to utilize a more efficient mechanism of retaining the spinal rods thereto.